it is a tough decision...
We decided to get a new puppy as a companion for our 2 year old dog, he always loved playing with the other dogs in the family, but they are hours away from us, so we don't visit constantly. We also felt it would be great to have 2 pups, and were ready for it.
The first couple months were very tough for us, as friendly as our big boy was, he didn't like the idea of a new kid in the house, now do take into consideration they had not met before we brought him home (error #1!) it was really hard, our older dog was depressed and very unhappy, to the point we were considering re-homing the little one.
It has now been almost 6 months since the puppy came home with us, and yes they fight sometimes, others they don't even want to be around each other, but for the most part I can say they love each other and are very good friends now... and I enjoy the 2 Knuckleheads very much
Would it be a possibility for you to bring the little guy home for a week or so to do a trial? maybe that will give you a better idea...